SUMMARY The United States (US) population is aging rapidly, with the age group over 65 years (y) the fastest growing segment. As average lifespan increases, the prevention or slowing of chronic disease and disability is a top public health priority. There is accumulating evidence that diet over the adult life course affects [risk for age- related declines in physical function, disability and mortality]. The study of dietary patterns is now a cornerstone of nutrition research and policy, with the most recent Federal dietary guidelines emphasizing overall dietary patterns, rather than nutrient specific recommendations. However, most epidemiological investigations concerning the health effects of different dietary patterns are cross-sectional; and most of the few studies with prospective design have information on diet only at baseline. Therefore, it remains unknown whether and to what extent adherence to recommended dietary guidelines during the adult life course is associated with [age-related declines in physical function, disability, and mortality]. We propose to address this gap in research by conducting a study to: (a) characterize dietary pattern trajectories across the adult life-span by examining adherence to existing dietary guidelines and recommendations, using the Healthy Eating Index- 2010, Alternate Healthy Eating Index-2010, (b) determine whether dietary pattern trajectories over the adult life course are associated with age-related changes in physical function including measures of mobility, muscle strength, [disability] and all-cause mortality in older age, and (c) using state-of-the-art causal inference methods for observational data, determine whether changes in dietary patterns over the adult life course is an causal risk factor for [age-related changes in physical function, disability,] and all-cause mortality throughout adulthood after taking into account mediation due to cardiovascular disease risk factors. [In addition, we will examine the associations between foods and data driven dietary patterns with age-associated declines, disability and all-cause mortality.]This study will be conducted in the NIA-supported Baltimore Longitudinal Study of Aging (BLSA). Initiated in 1958 the BLSA is the longest running scientific study of human aging, and one of the only US based longitudinal cohorts, that we are aware of, which has repeated assessments of diet, cardiovascular risk factors, and measures of mobility, muscle strength, physical function and disability using valid and accurate methods. Utilizing this cohort to answer our research questions is a highly cost-effective approach, as a wealth of data has already been collected. [Diet is a modifiable risk factor, and this study will provide evidence to determine whether adherence to recommended guidelines through adult life delays the onset of age-related functional declines and mortality.]